Method to produce flat vulcanized fibre sheets and coils



Dec. 2-6, 1967 E. J. SITES 3,360,427

METHOD TO PRODUCE FLAT VULCANIZED FIBRE SHEETS AND COILS I Filed Dec. 21, 1964 CrosS Machine (PRIOR ART) (PRIOR RT),

Cross Machine INVENTOR. EDWARD J. SITES BY ATTORNEY United States Patent ABSTRACT OF THE DISCLOSURE A process for manufacturing vulcanized fibre sheets includes forming a strip of paper with the basis weight of the paper being increased in small increments from the edges to the center. The basis weight at the center of the strip of paper is made one to eight percent greater than the weight at the edges. The paper is then vulcanized.

This invention relates to a new method of manufacturing vulcanized fibre and more particularly, concerns the processing of paper having a convex cross machine direction basis weight profile which substantially eliminates corrugations and distortions of portions of finished vulcanized fibre sheets and coils.

Vulcanized fibre is manufactured from various types of cellulosic fibers, for example, high alpha cellulose from Wood pulps or cotton. Heretofore, the cellulosic fibers were formed into a continuous ply of paper with a uniform cross machine basis Weight profile. A ply or a plurality of plies of paper depending on the desired thickness of the final ply of vulcanized fibre were saturated With a hydrolyzing agent, such as concentrated zinc chloride. The hydrolyzing agent was permitted to react on the cellulosic fibers for a predetermined amount of time at a controlled temperature. The hydrolyzing agent was removed from the paper in a series of leaching steps referred to as puring. The vulcanized fibre was then dried and calendered.

One of the major problems encountered in the manufacture of vulcanized fibre was the strong tendency of the cellulosic paper to vulcanize non-uniformly and form corrugated areas and flat areas causing the resulting product to have an appearance somewhat resembling a seersucker fabric. This corrugated condition is referred to as bagginess. Bagginess is highly undesirable for it renders the vulcanized fibre dilficult, if not impossible, to use by some consumers.

An example of the difiiculties which are encountered can be illustrated by problems presented to the manufacturer of abrasive sanding disks. In making abrasive sanding disks, one surface of the vulcanized fibre is coated with an adhesive. The coated vulcanized fibre is then given an elastrostatic charge of one polarity and passed over a belt carrying abrasive grit particles of the opposite polarity. Due to the opposite polarity of the grit and the vulcanized fibre, the grit is attracted from the belt to the coated surface of the vulcanized fibre. The amount and size of the grit attracted is dependent on the distance between the coated vulcanized fibre and the grit carrying belt. This distance must be constant in order to obtain a uniform distribution of grit particles. If baggy fibre is used, the distance between the surface of the fibre and the belt fluctuates due to corrugations in the vulcanized fibre and results in a non-uniform grit distribution. Sanding disks made from baggy vulcanized fibre are not satisfactory in that the non-uniform grit distribution causes the finishing disk to sand unevenly.

Accordingly, it is a general object of this invention to provide a novel method of manufacture for fiat vulcanized fibre.

It is a further general object of this invention to provide a novel method of manufacture of vulcanized fibre whereby the shrinkage of cellulosic paper during vulcanlzation is controlled permitting the formation of flat vulcanized fibre sheets and coils.

It is a more specific object of this invention to provide a method to produce a paper, which, when vulcanized, will yield flat vulcanized fibre.

Further objects and advantages will become apparent hereinafter and in the drawings in which:

FIG. 1 is a pictorial illustration of a prior art sheet of baggy vulcanized fibre produced from paper made according to the teaching of prior art.

FIG. 2 is an illustration of the cross section of a paper sheet having a uniform density and a substantially fiat cross machine direction basis weight profile as employed in the manufacture of the fibre illustrated by FIG. 1.

FIG. 3 is a pictorial illustration of a sheet of substantially flat vulcanized fibre made by the present invention.

FIG. 4 is an illustration of the cross section of a paper sheet having a uniform density and a convex cross machine direction basis weight profile employed in the present invention to manufacture flat vulcanized fibre.

Briefly, the objects of this invention are obtained by forming paper with a substantially convex cross machine direction basis weight profile, said paper being 18% greater in basis weight in the center than at the edges, and vulcanizing this paper in the conventional manner as described above.

'In describing the preferred embodiment of the invention illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is not intended to be limited to the specific terms so selected. It is to be understood that each specific term includes all technical equivalents which operate in a similar manner for a similar purpose. The term fiber is defined as a long, thread like cell or tissue whereas the term fibre is defined as being a sheet or a Web and not a single fiber.

Basis Weight is the weight per unit area. Cross machine basis Weight profile is the variation of the basis weight of paper as measured across the width of the paper sheet. The basis weight profile is determined by taking a plurality of uniform size samples of paper across the width of paper sheet and plotting the weights with respect to sample position. Fve or more samples should be taken at equidistant intervals across the Width of the paper sheet.

One of the more prevalent theories, before this invention, was that if a paper with a uniform cross machine direction basis weight profile was vulcanized, it would inherently form a fiat product.

As a result of an investigation into the causes of the baggy fibre condition, applicant found that this theory was incorrect. The applicant discovered that when a measured unit length of paper with a substantially fiat cross machine basis weight profile 18 was vulcanized, the resulting product 14 was baggier at the edges 10 than at the center 12; the resulting product being a classic example of baggy vulcanized fibre. Upon detailed analysis it was further discovered that the amount of shrinkage gradually increased from the edges to the center of the sheet. It was this variation of shrinkage during vulcanization that caused the edges of the sheet, the areas of relatively low shrinkage, to be baggier than the center portion of the sheet, and that excessive length at the edges had formed into corrugations 10 while the center areas 12 remained relatively flat.

From the above test applicant determined that vulcanized fibre making machines treat paper non-uniformly with progressively increasing shrinkage to the center of the machine and that bagginess is caused by the resulting non-uniform shrinkage.

Applicant discovered that the amount of shrinkage can be controlled by varying the basis weight of the paper. When the basis weight of the paper is decreased and all other variables held constant, the amount of shrinkage will increase. Applicant further found that if the basis weight of the paper was gradually increased from the edges, a, b to the center 0, a corrective factor was applied which compensated for the non-uniform shrinkage that was inherent in vulcanization process. More specifically, according to the teachings of this invention, when the cross machine direction basis weight profile of the paper was increased gradually from the edges a and b to the center with the center being one to eight percent greater in basis weight than the edges, the paper shrunk at a substantially uniform rate during vulcanization and flat vulcanized fibre 16 was produced. The one to eight percent limits are relatively critical in that if the basis weight variation is less than one percent, the effect of the increase in basis weight will be negligible and the inherent tendency to produce baggy fibre is still dominant. However, if the basis weight profile of the paper is increased substantially more than eight percent in the center portion, there will be such a decrease in the reactivity of the center portion that when the paper is vulcanized the center will become baggy and the edges will be flat. The preferred range of increase for the center portions of the basis weight profile is between four and six percent in that this range is easy to maintain and the optimum results are obtained in this range, with relatively little danger of accidently exceeding the one and eight percent limits.

As a further aid to understanding the invention, the paper makeup can be considered to be comprised of two integral portions, the first portion 20 being the major portion of the paper makeup having a flat cross machine basis weight profile. The second portion 22 has a substantially convex cross machine basis weight profile with the basis weight gradually increasing from the edges 24 and 26 to the center 28, the said basis weight at the edges 24, 26 approaching zero, and the basis weight at the center 28 being 18% of the basis weight of the first portion 20.

When either a single ply or a plurality of plies are to be vulcanized, the preferred method is to form each ply of paper with the specified convex cross machine basis weight profile. To obtain the specified convex cross machine basis weight profile, applicant employed an adjustable, flexible lip slice, and adjusted the lip of the slice so that the paper basis weight profile was formed according to the teaching of this invention. To do this, the central portions of the slice were opened up to permit a greater percentage of paper stock to flow to the center portions of the paper machine and the opening of the slice was gradually reduced to the outer edges to obtain the desired cross machine basis weight profile.

If a plurality of plies are to be vulcanized together, to form a single sheet of fibre an alternate method to obtain the desired profile is to use a combination of plies which when the individual basis weight profiles of the plies are averaged, the average basis weight profile will be according to the teachings of this invention. For example, it is possible to use a paper with a substantially flat cross machine direction basis weight profile 18 in combination with a paper with an extremely convexed cross machine direction basis weight profile and obtain flat vulcanized fibre if the average basis weight of the combination is within the range of this invention. This method is not the preferred method but will give the desired results and is within the scope of the invention.

It is to be understood that the form of the invention herewithin shown and described is to be taken as the preferred embodiment and that various changes may be made without departing from the scope of this invention. For example, the cross sections illustrated are of papers with a uniform density. It should be noted that the cross machine density of paper can be modified by calendering and that the paper with a substantially uniform cross sectional thickness can be produced from a paper with a convex basis weight profile but since the distribution of the basis weight of the paper will not be substantially modified by calendering, calendered paper is also within the scope of this invention.

Furthermore, it should be noted that the increase in basis weight in cross machine direction, as shown in the drawings, and as specified in the description, describes the basis weight profile as following a convex curve. It should be understood that this invention also includes methods whereby the basis weight is increased in relatively small increments, not exactly following a curve but with the average of the increments substantially approaching the convex profile as taught by this invention.

What is claimed is:

1. A process for the manufacture of flat vulcanized fibre sheets and coils comprising the steps of forming cellulosic fibers into a continuous strip of paper, increasing the basis weight of said paper in small increments from the edges of said paper strip to the center of said paper strip, said increasing of said basis weight being accomplished by employing an adjustable, flexible lip slice and adjusting the lip of the slice to provide predetermined basis weights in said paper, said basis weight at said center being one to eight percent greater than said basis weight at the edges and vulcanizing the said paper strip, said step of vulcanizing including saturating said fibre with a hydrolyzing agent and removing said hydrolyzing agent in a series of leaching steps.

2. The process substantially as described in claim 2 wherein said basis weight at the said center is four to six percent greater than said basis weight at said edge.

References Cited UNITED STATES PATENTS 2,286,968 6/1942 Landt 8-119 2,928,464 3/1960 Western et al. 162347 3,203,850 8/1965 McCarty 162113 S. LEON BASHORE, Primary Examiner. 

1. A PROCESS FOR THE MANUFACTURE OF FLAT VULCANIZED FIBRE SHEETS AND COILS COMPRISING THE STEPS OF FORMING CELLULOSIC FIBERS INTO A CONTINUOUS STRIP OF PAPER, INCREASING THE BASIS WEIGHT OF SAID PAPER IN SMALL INCREMENTS FROM THE EDGES OF SAID PAPER STRIP TO THE CENTER OF SAID PAPER STRIP, SAID INCREASING OF SAID BASIS WEIGHT BEING ACCOMPLISHED BY EMPLOYING AN ADJUSTABLE, FLEXIBLE LIP SLICE AND ADJUSTING THE LIP OF THE SLICE TO PROVIDE PREDETERMINED BASIS WEIGHTSIN SAID PAPER, SAID BASIS WEIGHT AT SAID CENTER BEING ONE TO EIGHT PERCENT GREATER THAN SAID BASIS WEIGHT AT THE EDGES AND VULCANIZING THE SAID PAPER STRIP, SAID STEP OF VULCANIZING INCLUDING SATURATING SAID FIBRE WITH A HYDROLYZING AGENT AND REMOVING SAID HYDROLYZING AGENT IN A SERIES OF LEACHING STEPS. 